Fluid shock absorber struts which are used in a vehicle suspension system often experience a bending moment caused by the offset of the tire contact patch with the roadway from the strut centerline. This offset loading increases the sliding friction between the piston rod and surrounding cylinder, increasing harshness and reducing the life of the shock absorber strut. One of the most commonly used means to counteract this offset loading on a fluid shock absorber strut such as a McPherson strut, is by the use of a system wherein a counter lateral force is exerted on the strut by the use of an offset or angled coil spring surrounding the piston rod and cylinder.
Some examples of prior art suspension systems which attempt to overcome this offset loading problem are shown in the following patents.
U.S. Pat. No. 3,954,257 discloses a suspension system in which the extended end of the piston rod is connected to the underside of an upper spring and bearing assembly positioned within a suitable bracket connecting the suspension system to the vehicle. This suspension unit includes a surrounding helical spring and a rolling flexible diaphragm member connected to a periphery of a housing in which a fluid shock absorber cartridge is mounted with the upper end of the flexible diaphragm being connected to a spring retaining ring.
U.S. Reissue Pat. No. 31,184 discloses another suspension system which attempts to reduce this offset loading problem by the use of an elastomeric mounting arrangement at the extended end of the piston rod in combination with a surrounding coil spring. German Patent No. 2,100,338 discloses another suspension system in which the piston rod of a fluid shock absorber is set at an offset angle to match the suspension system in order to counteract the heretofore unbalanced forces exerted thereon.
Another type of vehicle suspension system uses pneumatic springs commonly referred to as air springs in place of a fluid shock absorber. In these air springs one or more pistons act within a chamber filled with a pressurized fluid or gas causing compression and expansion of the fluid contained in the pressure chamber, to absorb the road shocks as the pistons move between jounce and rebound positions. Some examples of prior art vehicle air springs are shown in U.S. Pat. Nos. 2,926,011; 2,985,445; 2,978,256; 3,046,000; and 3,074079.
Therefore, the need exists for a suspension system using a fluid shock absorber strut in combination with means for offsetting the off center lateral forces exerted on the shock absorber strut. There is no known suspension system of which we are aware which accomplishes this by the combination shock absorber strut/air spring suspension system in which the air spring is provided with means of exerting an offset loading to counteract the bending moment caused by the unbalanced load exerted on the shock absorber strut and without interfering with the tire when in the jounce position.
Another problem that exists with suspension units using a fluid shock absorber strut in combination with an air spring is the ability to provide dual path isolation in a compact package or unit on a steerable air strut. Dual path isolation means that the strut shaft or piston rod is separately isolated by an elastomeric material from the air spring, and in particular the air canister component thereof, and that the canister also is isolated by an elastomer from the vehicle chassis. Heretofore, dual path isolators have been used to reduce ride harshness and noise in strut type applications, but not in combination with an air spring. Some examples of dual path type isolators are shown in U.S. Pat. Nos. 4,248,454; 4,256,292; 4,298,193; 4,319,768; 4,434,977; 4,478,396; 4,531,759 and French Patent No. 2401-787. Also, shock absorbing struts have been used in combination with air springs, such as is shown in U.S. Pat. Nos. 4,555,096; 4,592,540; 4,518,154 and 3,954,257, and Japanese Patent No 241538. However, these assemblies do not provide dual path isolation.
Likewise, none of these known prior art suspension systems show a unit in which a shock absorber strut is combined with an air spring wherein the air canister portion of the air spring is separated from the vehicle chassis by a primary elastomeric isolator, in combination with a bearing which allows the dual isolation to be used on a steerable air strut together with a secondary elastomeric isolator which separates the air canister from the piston rod of the shock absorber; and in which the secondary isolator also functions as a nonrotatable air seal for one open end of the air spring, in a compact unit as is the present invention described in detail below and set forth in the claims.